A PON (Passive Optical Network) system is generally composed of an office-side OLT (Optical Line Terminal), a user-side ONU (Optical Network Unit)/ONT (Optical Network Termination) and an ODN (Optical Distribution Network). The ODN consists of single-mode optical fibers, optical splitters, optical connectors and other passive optical components and provides an optical transmission medium for the physical connection between the OLT and the ONU. The ODN generally adopts a point-to-multipoint structure, i.e. an OLT is connected to multiple ONUs via an ODN.
An EPON (Ethernet Passive Optical Network) is a new-generation broadband passive optical integrated access technology based on IEEE (Institute of Electrical and Electronics Engineers) 802.3-2005 Section 5 and IEEE802.3av standards.
For the EPON, the IEEE standards only define the standards of physical layers and link layers of a 1G-EPON and a 100-EPON and do not involve other service functions. For multicast, the IEEE802.3-2005 Section 5 standard defines the identification of a broadcast logical channel in the 1G-EPON as 0×7fff; the IEEE802.3av standard defines the identification of a broadcast logical channel in the 10G-EPON as 0×7ffe. Generally, when an OLT in the EPON transmits a broadcast and multicast message, it may transmit data to all ports under a PON port by using a broadcast logical channel; then the ONU determines a port to which the broadcast and multicast message will be forwarded in accordance with a locally saved table illustrating correspondences between a multicast group and local user interfaces.
The above is mainly for the circumstance that only the same type of ONUs are connected to a same port on the OLT.
FIG. 1 is a schematic diagram of networking in the prior art when 1G-EPONs and 10G-EPONs coexist. As shown in FIG. 1, there are 3 ONUs under optical splitter 1 connected to port 1 of an OLT, wherein ONU A and ONU B are 1G-EPON ONUs, and ONU C is a 10G-EPON ONU. When ONUs at different rates are connected to a same port of a same OLT, the existing standards do not have the provisions on how an OLT uses a broadcast or multicast logical channel to transmit downlink broadcast packets and multicast control messages, so how to efficiently utilize a physical channel in a PON to realize the forwarding of downlink broadcast packets and multicast control messages is a problem to be solved.